1. Field of the Invention
The invention relates to graphite foam material, of the type used for high temperature insulation and the like, and to a method of making the same. The invention also relates to a graphite material that may be used and added to provide protection from electrostatic discharge (ESD) or shielding from electromagnetic and radio interference (EMI/RFI).
2. Art Background
In the prior art, various forms of graphite material have been used as insulating materials in high temperature applications including industrial ovens and furnaces, vacuum furnaces and controlled atmosphere heating apparatus and the like.
One of the first such graphite insulating materials was powdered carbon black which had an appropriate amount of insulating capacity, but was very difficult to handle, relatively heavy, and extremely time consuming to replace. As a result with the advent of foam and resin chemistry, a number of newer materials were developed which were lighter and easier to handle, but which had the requisite insulating capacity. One such material is a carbon fiber insulating material made of a carbon fiber held in a matrix by a phenolic resin material, and formed into a board or block.
Static electricity and electrostatic discharge (ESD) are naturally occurring phenomena. Simply stated, static electricity is electrical energy at rest on a surface. It is generally created by the rubbing together and separating of two materials, one of which is usually non-conductive. Typically, one material gives up electrons and becomes positively charged; the other takes on the electrons and becomes negatively charged. ESD may be defined as the sudden discharge of an electrostatic potential from one body to another. A good example may be the shock one receives when touching a metal door knob after walking across a carpeted floor.
In many environments, ESD may damage or destroy sensitive electronic components, erase or alter magnetic media, or set off explosions or fires in flammable environments. These discharges may be caused by a variety of sources, most commonly there is a direct discharge from a person or equipment into a sensitive object.
One way of preventing ESD is to reduce the generation of charges in the first place. A second way of preventing ESD is to provide a ground path for the safe dissipation of accumulated charges to ground. A third method is to provide shielding or protection of devices and equipment from discharge through packaging. ESD may also be controlled with materials, such as conductive plastics, that do not generate high levels of charge, that dissipate charges before they accumulate to dangerous levels, or that provide electrostatic shielding to prevent charges from reaching the sensitive product.
Electromagnetic Interference (EMI) is electrical energy, either electromagnetic or in the radio frequency (RF) range in the case of radio frequency interference (RFI) that is radiated by specific sources. Some of these sources include computer circuits, radio transmitters, fluorescent lamps, color TV oscillators, electric motors, automotive ignition coils, overhead power lines, lightning, TV games, and many other resources. EMI/RFI may interfere with the operation of simple household appliances such as causing the unwanted operation of garage door openers. On another level, EMI/RFI may corrupt data in large scale computer systems, cause inaccurate readings and output in aircraft guidance systems, and interrupt the functioning of medical devices, such as pacemakers.
Proper shielding may prevent products from emitting electromagnetic or radio frequency energy to other susceptible equipment. Shielding may also protect susceptible equipment from the effects of externally radiated EMI/RFI as the shielding absorbs the energy emitted, converting it to thermal energy.
EMI thermoplastic composites are used primarily for shielding against emission or reception of EMI and RFI. Traditionally, shielding has been accomplished by encasing sensitive electronic parts in metal housings or by using metallic coatings on the inside of plastic housings. Thermoplastic compounds with appropriate shielding additives are cost effective alternatives in many applications due to their ability to take on complex shapes and maintain tight tolerances.
It is desirable to provide, at relatively low cost, a compound/s that may dissipate charges before they accumulate to dangerous levels, that provide electrostatic shielding to prevent charges from reaching the sensitive product. Moreover, it is desirable to provide, at relatively low cost, a material for shielding against emission or re-emission of electrostatic.